1. Field of the Invention
The present invention generally relates to an on-chip CMOS spectrum analyzer for performing diagnostics on signals using digital autocorrelation of coarsely quantized signals.
2. Description of the Related Art
In analog and mixed-signal communication circuits, it is often desired to measure the frequency spectrum of a circuit element. This might be needed, for example, in studying a PLL (phase locked-loop) to see if the frequency is at its required value, to study its phase noise, and to see if there is any crosstalk from noise sources with nearby frequencies. This measurement is generally done by bringing the signal of interest off the chip via a dedicated I/O pin and measuring its frequency content on an external spectrum analyzer (SA). This I/O pin must be connected to the circuit of interest via a high bandwidth driver which does not distort the signal to be measured. In general, this imposes a limit on the number of internal signals which can be measured. In a situation where there is an array of such circuits, such as a parallel bus of data channels all operating at similar, but not identical, frequencies, the measurement by this method requires multiple connections and disconnections. Thus, the measurement is time-consuming and not suitable for rapid testing. Furthermore, the number of points which can be measured is limited by the number of I/O pins which can be dedicated to this purpose.